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I've just fitted a Belkin USB 2.0 USB card in a Blade 2000 running
Solaris 10 update 5. (At least I was expecting it to be USB 2, but now I
find Solaris is going to use it only as USB 1 - see my other post for
more on this.)

Anyway, forgetting the speed issues for the moment, I attached a pair of
Western Digitial "My Book Essential Edition" 1 TB external USB disks.
The disks were both bought from Amazon within a week of each other, and
for all intents are purposes look the same.

I can create a ZFS pool for each disk individually, and they are the
same size (as expected), since the disks are as far as I am aware identical.


# zpool create tmp1 c6t0d0
# zpool create tmp2 c7t0d0
# zpool list
NAME SIZE USED AVAIL CAP HEALTH ALTROOT
tmp1 928G 88K 928G 0% ONLINE -
tmp2 928G 88K 928G 0% ONLINE -



df shows two file systems of the same size.

Filesystem kbytes used avail capacity Mounted on
<snip>
tmp1 957874176 24 957874091 1% /tmp1
tmp2 957874176 24 957874091 1% /tmp2


Now I destroy the pools.

# zpool destroy -f tmp1
# zpool destroy -f tmp2


Finally I try to mirror them.

# zpool create TBmirror mirror c6t0d0 c7t0d0
invalid vdev specification
use '-f' to override the following errors:
mirror contains devices of different sizes


Now I can create the mirror if I use the -f option


# zpool create -f TBmirror mirror c6t0d0 c7t0d0
# zpool list
NAME SIZE USED AVAIL CAP HEALTH ALTROOT
TBmirror 928G 89K 928G 0% ONLINE -

Again, using df I see the mirror is the exact same size as the
individual disks were.


# df -k
Filesystem kbytes used avail capacity Mounted on
/dev/dsk/c1t1d0s0 20168929 15875917 4091323 80% /
<snip>
TBmirror 957874176 24 957874090 1% /TBmirror

Any ideas why a warning/error is generated by zpool for two apparently
identical external USB disks?